Fix workspaced junctions

This branch does a few things:

• Use Element._consistency() when checking the consistency of the junction

  This is the canonical way for checking consistency, and will include an alternative check if the element is workspaced.

• Use Element._fetch() to automatically fetch junction elements, rather than reimplementing this in the loader.

  This is the canonical way for fetching an element's sources, better not reimplement it here. Also the Element._fetch() technique will properly leverage SourceCache.

• Adds regression test for #1030 (closed)

This branch fixes #1030 (closed)